This specification relates to selectively requesting cached resources.
The Internet enables access to a wide variety of resources, such as video or audio files, images, and web pages for particular subjects. Each resource has a corresponding resource address that is used to locate the resource on the Internet. Resources may be hosted on a server that is connected to the Internet, and each resource may also be associated with a domain. When a user directs a user device to request a resource, often using a web browser or other application on the user device, the user device sends a resource request to the server identified by the resource address. Upon receipt of the resource request, the server attempts to locate the requested resource and provide it to the requesting user device.
Often, however, the server is unable to locate or provide the requested resource for any number of reasons. In these situations, the user will not be provided with the requested resource, and is often presented with an error page. Error pages are often vague and unhelpful to the user, generally only listing a standard error status code. However, a publisher of the resource (or the publisher of the domain associated with the resource) may provide a customized error page with helpful information. For example, a publisher may decide to remove a resource or section of a website, and may provide information indicating that the resources are no longer available in response to the requests for the resources that have been removed. In other situations, the resource request may never be received by the server, in which case the publisher will not be able to provide the user device with the requested resource or a customized error page. As a result, a user is often presented with vague and unhelpful error pages, or receives no content, when requesting a resource that is unavailable.